A New Chromogenic Medium for Rapid Detection of Vibrio Species

Begin with broths containing actively growing cultures of Vibrio species, a Gram-negative bacterium, along with non-Vibrio species.

Streak these cultures onto thiosulfate-citrate-bile salts-sucrose or TCBS agar and chromogenic agar. Incubate.

Both TCBS and chromogenic agars have a high pH and bile salts that support the growth of salt-loving Vibrio species while inhibiting non-Vibrio species.

On TCBS agar, sucrose-fermenting Vibrio species metabolize sucrose to produce acid that lowers the pH, turning colonies yellow, while non-fermenters form blue-green colonies.

However, color changes in the surrounding medium can obscure colony morphology, reducing specificity.

In contrast, chromogenic agar contains substrates that react with species-specific enzymes, producing distinctly pigmented colonies without altering the medium's color.

Observe colony morphology and pigmentation on both media under ambient and UV light to differentiate Vibrio species.

Due to its enzyme-based differentiation, chromogenic agar more accurately distinguishes Vibrio species, making it superior to TCBS agar.

To grow out the colonies of interest on selective and differential media, transfer a few isolated colonies into five milliliters of the appropriate broth and reincubate the cultures at 35 to 37 degrees Celsius for 16 to 24 hours. The next day, streak a loopful of the overnight cultures onto at least one thiosulfate-citrate-bile salts-sucrose or TCBS, agar plate, and at least one chromogenic agar plate for up to 96 hours of incubation at 35 to 37 degrees Celsius. At the end of the incubation, examine both the culture density on the plate and the size of the isolated colonies to determine the overall growth of the strains, recording the color of the colonies under ambient or UV light, as appropriate, and noting any other important characteristics of the colonies.